Exploiting Hydrazones To Improve the Efficiency of 6π-Electrocyclization Reactions of 1-Azatrienes

Abstract

The greater geometric lability of hydrazones over oxime ethers is used as a basis to overcome the reluctance of Zoxime ether azatrienes to undergo electrocyclization towards the synthesis of borylated (heteroaromatic) pyridines and ring-fused analogs. Such hydrazones now allow access to previously inaccessible tri-and tetrasubstituted 3-borylpyridines in high yields.The prominence of heteroaromatic motifs in pharmaceutical agents, agrochemicals and functional materials has motivated synthetic chemists to devise new strategies for the efficient and selective incorporation of these fragments into a broad range of molecular scaffolds. In this regard, boronic acid chemistry provides one of the most widely used approaches Scheme 1. Dependence of electrocyclization efficiency on oxime ether stereochemistry for the coupling of heteroaromatic systems because of the synthetic versatility of these compounds. 1

Gold(I)‐katalysierte Intramolekulare 7‐endo‐dig Zyklisierung von Trien‐In‐Systemen: Neuer Zugang zu Azulenothiophenen

“…Die Autoren haben in den Hintergrundinformationen weitere Literatur zitiert. [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]…”

Gold(I)‐Catalyzed Intramolecular 7‐endo‐dig Cyclization of Triene‐Yne Systems: New Access towards Azulenothiophenes

“…The authors have cited additional references within the Supporting Information. [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]…”

Pseudopericyclic Dearomative 1,6‐Cyclization of 1‐(2‐Pyridyl)‐2‐azabuta‐1,3‐dienes: Synthesis and Ring–Chain Valence Equilibria of 4H‐Pyrido[1,2‐a]pyrazines

“…The aza‐1,6‐electrocyclization is a powerful and atom‐economic approach to the formation of N‐heterocyclic compounds such as pyridines, quinolines, and isoquinolines, including natural products and medicines Thus, the 1,6‐electrocyclization of 1‐aza‐, 2‐aza‐, and 3‐azahexa‐1,3,5‐trienes leads to the formation of 1,2‐, 2,3‐, and 3,4‐dihydropyridines (Scheme , reactions 1–3). Such cyclization easily occurs when none of the double bonds of the azatriene fragment are included in the aromatic cycle.…”

“…Such cyclization easily occurs when none of the double bonds of the azatriene fragment are included in the aromatic cycle. [2a], [2b], [2c], [2d], [2e], [3a], [3b], [4a], [4b], [4c], [4d], When one of the double bonds of starting azatriene is a part of an aromatic system, 1,6‐electrocyclization can occur reversibly (if aromatization of the primary dihydropyridine product is impossible) or irreversibly (if aromatization of the primary dihydropyridine intermediate into pyridine is plausible). [2f], [2g], [2h], [2i], [2j], [3c], [3d], [3e], [3f], [4e]…”